Drive control and hold-in arrangement for a rotary actuator

ABSTRACT

A rotary actuator of the type in which a ring gear is orbited within a stationary reaction gear and about an output gear, the ring gear driven to so orbit by a torque producing vector which is constantly indexing about the circumference thereof to produce its orbiting motion is disclosed, in which an arrangement is provided for producing a hydraulically generated hold-in vector acting on the ring gear at an angle displaced from the torque producing vector and which also constantly indexes about the circumference thereof in the same manner so that the ring gear is maintained in engagement with the reaction and output gear during its orbiting motion without the use of rotary bearings or cranks. This arrangement also provides for a disengagement of the ring gear from the reaction and output gear in the event a hold-in vector of a certain magnitude is not produced to thus provide a means to controllably discontinue drive through the unit.

United States Patent [191 Read et al. 9

[ 1 May 29, 1973 DRIVE CONTROL AND HOLD-IN ARRANGEMENT FOR A ROTARYACTUATOR [75] Inventors: Ronald C. Read, Birmingham; Norbert L. Sikora,Southfield; Kenneth W. Verge, Farmington, all of Mich.

[73] Assignee: The Bendix Corporation, Southfield,

Mich.

[22] Filed: July 1, 1971 [21] Appl. No.: l58,757

[52] US. Cl ..418/60, 418/61 [51] Int. Cl ..F0lc 1/02, F03c 3/00, F0401/02 [58] Field of Search ..4l8/60, 61, 210, 418/212, 213

, [56] References Cited UNITED STATES PATENTS 1,969,651 8/1934Kretschmer ..4l8/61 3,383,931 5/1968 Patterson ..418/6l 3,389,618 6/1968McDermott... ..4l8/6l 3,574,489 4/1971 Pierrat ..4l8/6l 3,453,966 7/1969Eddy ..4l8/6l 3,490,383 1/1970 Parrett... ..418/6l FOREIGN PATENTS ORAPPLICATIONS 398,678 9/1933 GreatBritain ..4l8/60 1,026,500 2/1953France ..4l8/6l Primary Examiner-Carlton R. Croyle AssistantExaminer-John J. Vrabuk A ttorney-John R. Benefiel; Plante, Hartz, Smith& Thompson [57] ABSTRACT A rotary actuator of the type in which a ringgear is orbited within a stationary reaction gear and about an outputgear, the ring gear driven to so orbit by a torque producing vectorwhich is constantly indexing about the circumference thereof to produceits orbiting motion is disclosed, in which an arrangement is providedfor producing a hydraulically generated hold-in vector acting on thering gear at an angle displaced from the torque producing vector andwhich also constantly indexes about the circumference thereof in thesame manner so that the ring gear is maintained in engagement with thereaction and output gear during its orbiting motion without the use ofrotary bearings or cranks. This arrangement also provides for adisengagement of the ring gear from the reaction and output gear in theevent a hold-in vector of a certain magnitude is not produced to thusprovide a means to controllably discontinue drive through the unit.

22 Claims, 13 Drawing Figures PATENTED HAYES I975 SHEET 1 [1F 5INVENTORS RONALD G- READ NORBERT L. SIKORA KENNETH W- VERGE ATTORNEYPATENTEU 3.736.078

SHEET '4 [1F 5 mvsmoRs FIGS RONALD e. READ NORBERT L. s||

KENNETH w. vs

. BY M R 8W ATTORNEY PAIENIEWZ 3,736,078

SHEET 5 OF 5 lNVENTORS RONALD G. READ NORBERT L. SIKQRA KENNETH W. VERGEBY 4;, H

ATTORNEY DRIVE CONTROL AND HOLD-IN ARRANGEMENT FOR A ROTARY ACTUATORBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionconcerns rotary actuators and more particularly, rotary actuators of theeccentric rotor type.

2. Description of the Prior Art In many applications of rotaryactuators, a relatively high reliability decoupling capability is verydesirable, and for such applications, such capability should be possiblewithout compromising the basic simplicity and size of the device.Conventional rotary clutch arrangments add bulk and complexity andcomprise reliability so that as a result rotary actuators have notoffered the overall simplicity and reliability of linear fluid actuatorshaving this capability. Such clutch arrangements also may introducepower losses as the actuator elements that are not decoupled willcontinue to be driven by the power source.

In addition, in rotary actuators of the type described in US Pat. No.3,5 l4,765 the geometry of the gear set and the pressure angle of thegear teeth is such that the reaction of the output gear to the drivingtorque exerted by the orbiting member normally creates a demeshing forcetending to disengage the orbiting member from the output gear with whichit is normally engaged. Conventional arrangements support the orbiter onrotary bearings mounted on an eccentric member to withstand the force aswell as to provide the driving force required to orbit this element orprovide other structural constraints of the motion of the orbitingmember.

In the aforementioned patent which discloses a rotary hydraulic forcevector to provide the orbital forces, a system of absorbing thisreaction on the flanks of the gear teeth spaced on either side of thedemeshing vector is utilized.

In the conventional approach, the use of such rotary bearings increasespower losses, complicates the design, increases manufacturing andservicing costs, and increases the inertia of the unit.

In the approach disclosed in the references U.S. patent, tooth wear maybe a significant drawback in certain high tooth load applications.

Hence, it is an object of the present invention to provide a highlyreliable and simple decoupling arrangement for such a gearset which doesnot involve significant power losses in the decoupled state.

Another primary object is to provide an arrangement for providing ahold-in force to counter the demeshing reaction which does not involverotary bearings on the orbiting element or excessive reaction toothloadings on the flanks of the gear teeth.

SUMMARY OF THE INVENTION These and other objects which will becomeapparent upon a reading of the following specification and claims areaccomplished by providing a rotating hold-in vector acting on theorbiter along the eccentricity axis and at an angle to the torqueproducing vector and rotating about the gear set during orbiting in thesame manner as the torque producing vector. In the event the hold-invector is removed or declines to a certain predetermined minimum, thedemeshing forces are allowed to disengage the orbiter from the outputgear to thus discontinue drive through the unit.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a specific embodiment ofan actuator according to the present invention of a section taken alongthe longitudinal axis thereof.

FIG. 2 is a paritally sectional view of the actuator shown in FIG. 1.

FIG. 3 is an enlarged view of the section taken along the line 3-3 inFIG. 1.

FIG. 4 is a diagrammatic representation of the torque producing vectorproduced by the porting arrangement shown in FIG. 3.

FIG. 5 is a view of the section taken along the line 55 in FIG. 1.

FIG. 6 is a view of the section taken along the line 6-6 in FIG. 1. I

FIG. 7 is a view of the section taken along the line 7-7 in FIG. 6.

FIG. 8 is an enlarged view of the section taken along line 88 in FIG. 1.

FIG. 9 is a diagrammatic representation of the holdin vector produced bythe porting arrangement shown in FIG. 8.

FIG. 10 is a view of the section taken along the line 10-10 in FIG. 1.

FIG. 11 is a view of the section taken along the line 11l1 in FIG. 1.

FIG. 12 is a view of the section taken along the line l2--12 in FIG. 1.

Fig. 13 is a sectional view of the position of the centering pistons inthe decoupled condition of the actuator shown in FIGS. 5 and 10 in thedriving condition of the actuator.

DETAILED DESCRIPTION In the following detailed description, certainspecific terminology will be utilized for the sake of clarity andspecific embodiments will be described in order to provide a completeunderstanding of the invention, but it is to be understood that theinvention is not so limited and may be practiced in a variety of formsand embodiments.

Referring to the Drawings, and particularly FIG. 1, an actuator 10according to the present invention is depicted in longitudinal section,which includes an externally toothed output shaft 12 supported at eachend by bushings 14 and 16 disposed in front and rear cover plates 18,20, respectively.

The output shaft 12 which has integral output gear external teeth isdriven by a ring gear assembly 22 which includes an internally toothedsleeve 24 eccentrically positioned with respect to the output shaft 12(See FIGS. 3 and 8) and meshing therewith. I

Fixed to sleeve 24 are a pair of torque producing motor rings 26 and 28and an intermediate hold-in motor ring 30. The gear and sleeve assembly22 is orbited about the output shaft 12 axis by means of a pair of fluidmotors 32 and 34 described infra in detail acting on the motor rings 26and 28, while the force required to maintain the internally toothedsleeve 24 in mesh with the externally toothed output shaft 12 againstthe demeshing forces generated by the tooth pressure angles and thereaction of the load to the torque produced is provided by a'fluid motor36 also described in detail infra and acting on the hold-in motor ring30. As discussed supra, such an arrangement is necessary since theassembly 22 is not structurally constrained to move in the orbit aboutthe output shaft 12 axis but rather floats in the plane of its orbitalmotion in order to eliminate the inertia, friction and expense ofbearing, crank or other such arrangments.

Referring to FIG. 3, the torque producing fluid motor 32, which istypical of both motors 32 and 34, is shown in detail, and includes aninternally toothed reaction gear 38 which has the same number ofinternal teeth 40 machined therein as the gear 26 external teeth 42, butwhich are somewhat larger as shown to accommodate the orbiting movementof the gear 26 within the reaction gear 38 and about the output shaft 12axis.

A plurality of fluid actuation chambers 44, 46, 48, 50, 52, 54, 56, 58,and 60 are defined by the interior of the reaction gear 38, the exteriorof the gear 26, and the space between a series of sealing vanes 62.

The sealing vanes 62 are retained at one end in sockets 64 beveled at 66to allow swiveling movement of the vanes and disposed in slots 68 at theother end to allow both swiveling and sliding movement therein. Thus asthe gear 26 orbits, the vanes move in and out of the slots and swivel toaccommodate the relative movement between the reaction gear 38 and gear26 while still preventing fluid from passing from one chamber to theother.

The chambers 44-60 are defined axially by a porting plate 70 on one sideand a manifold 72 on the other, both of which are sealed to the reactiongear 38 at 74 and 76.

Each chamber of the torque producing motor 32 communicates with aradially extending slot 78 axially relieved into one side of theexternal gear 26 as shown in FIG. 1 and passing into the space betweenthe teeth 42 to provide a fluid access to each chamber 44-60.

Each chamber 44-60 has an associated supply port 80 and return port 82with the communication therebetween controlled by the registry of eachslot 78 therewith, which is in turn controlled by the relative positionof the gear 26 with respect to the porting plate 76.

The supply ports 80 are provided with a source of high pressure fluidvia passages 84 which communicate with a supply annulus 86 (FIGS. 1,l2), groove 88 formed in the end plate 90, passage 92 (FIGS. 1, 11)formed by a series of aligned openings in the various plates and gears,groove 94 and recess 96 in manifold 98. Recess 96 is supplied with highpressure fluid via inlet port 100 (FIG. adapted to receive a fitting andhigh pressure line (not shown) from a source of fluid under pressure(also not shown).

The return ports 82 communicate via passages 102 with a return annulus104 formed in the end plate 90, in turn communicating with passage 106formed by aligned openings in the various plates and gears in the samefashion as passage 92.

Passage 106 communicates with groovel08 and recess 110 in manifold 98.Recess 110 in turn passes into outlet port 1 12 which is adapted toreceive a fitting and return line (not shown) to the sump (also notshown).

Similar arrangements are provided in end plate 20, porting plate 114,and gear 28 so that the chambers associated with torque motors 34 areplaced in communication with the source and the sump in the same manner.

The ports 80 and 82 and the slots 78 are so placed that as the gear 26orbits about the axis of the output gear 12, the slots 78 come intoregistry successively with the supply ports 80 and then the exhaustports 82 as a result of the circumferential or angular relativedisplacement between the porting plate allowed by the clearance betweenthe external teeth 42 and internal teeth 40. Hence, at any givenposition, the chambers on one side of the eccentricity axis arepressurized and those on the other side are connected to the lowpressure region. For example, in the position shown, chambers 58, 60, 44and 46 are pressurized since the slots 78 are uncovering all the supplyports of these chambers. Chambers 50, 52, 54, and 56 are depressurizedsince the slots 78 are at least paritally uncovering these ports asshown. The net result is a fluid force (shown schematically in FIG. 4)acting on the gear 26 (and the rest of the assembly 22) in the directionso as to cause it to move about the axis of the gear 12 as indicated inFIG. 3. As the gear 26 moves, the slots successively uncover and coversupply and exhaust ports 80 and 82 due to the shifting circumferentialor angular relative position of the porting plate 70 and gear 26 so thatan orbiting movement of the gear 26 axis about the axis of the outputgear 12 results which movement will drive the output gear 12 by virtueof its meshing engagement of sleeve 24 secured to gear 26.

Ring 28 is similarly driven by fluid motor 34 so as to move insynchronism therewith and add to the torque produced by the ring 26.This arrangement produces an axial force balance within the unit toeliminate tipping of the ring gear assembly 22 which could be caused bya couple set up between a single torque motor and hold-in motor.

As this general type of actuator is now known in the art and isdisclosed in US. Pat. No. 3,516,765, assigned to the assignee of thepresent application, a detailed analysis of the ratios obtained andother characteristics thereof is not here included for the sake ofsimplicity.

The torque exerted by the assembly 22 and the reaction of the loadcoupled to the output gear 12 will createa demeshing force as acomponent produced by the particular pressure angle of the teeth of theoutput gear 12 and sleeve 24 as discussed infra.

As discussed supra, in order to maintain the sleeve 24 in engagementwith the output shaft as well as to provide an advantageous method ofdiscontinuing drive through the unit 10, the actuator according to thepresent invention includes a separate fluid motor 36 acting on hold-inring 30.

Ring 30 also fixed to sleeve 24 has external gear teeth 116 formedthereon and is disposed within a reaction gear 118 having the samenumber of internal teeth 120 formed therein, but of a larger size aswith the torque gears 26 and 28 so as to allow orbiting movement of gear30 within the gear 118 without rotation thereof.

It is noted that the geared relationship between ring 30 and reactiongear 118 may be eliminated, since the reaction forces may be completelyabsorbed by the reaction gears of the torque motors 32, 34.

The fluid motor 36 includes a plurality of actuation chambers 122, 124,126, 128, 130, 132, 134, 136, and 138 (FIG. 8) which are defined by thespaces between reaction gear 118 and hold-in gear 30 subdivided by aplurality of sealing vanes 140, retained in sockets 142 in hold-in gear30 and slots 144 in the reaction gear 1 18 so as to prevent fluid frompassing therebetween during orbiting movement of the hold-in gear 30.The chambers 122-138 are defined axially by porting plate 146 and coverplate 148 sealed to the reaction gear 118 at 150 and 152.

Communication with the chambers 122-138 is controlled by a series ofgenerally U-shaped slots 154 recessed into the face of hold-in gear 30and opening into the relieved area 156 (FIG. 1) on the external teeth116. The slots 154 come into and out of registry with a radially offsetseries of supply and return ports 158 and 160 circumferentially spacedon a center line aligned with the output gear axis as the reaction gear30 orbits as a result of the resulting relative radial or inand-outmovement between the center line of the parts in porting plate 146 andhold-in gear. Thus, at any position such as that shown in FIG. 8, aportion of the chambers 122-138 are pressurized and the remainder aredepressurized.

Supply ports 158 communicate with passages 162 (FIGS. 1, 8) in portingplate 146 which in turn communicates with a supply annulus 164 (FIGS. 1and 6) which is supplied with fluid under pressure via passage 166opening into inlet port 168 (FIGS. 2, 5) adapted to receive a fittingand high pressureline (not shown) to a source of fluid under pressure(also not shown).

The return ports 160 are connected to the return via passages 170 inporting plate 146 which open into a return annulus 172 in manifold 72(FIGS. 1, 6) which in turn is connected via passage 174 (FIGS. 2, 5) tooutlet port 176 adapted to receive a fitting and return line to the sump(not shown).

The U-shaped slots and the supply and return ports 158 and 160 arepositioned so that as the hold-in gear 30 is orbited about the axis ofthe output gear 12 the in-and-out movement causes a progressive coveringand uncovering of the supply and return ports 158 and 160 such that afluid pressure is applied to the hold-in gear 30 by means of the fluidactuation chambers 122-138 in the direction along the eccentricity axis,tending to hold the sleeve 24 and output gear 12 in mesh as indicated inFIG. 9. As the reaction gear 30 orbits the progressive covering anduncovering of the ports 158 and 160 causes the line of action of thisfluid force to constantly shift so that as the meshing point changes,the force generated is always directed so as to hold these gears inmesh.

In the position shown in FIG. 8, chambers 132, 134, 136, and 138 arepressurized, while chambers 122, 124, 126, 128, and 130 aredepressurized to produce the hold-in force indicated in FIG. 9. As thegear orbits from the position shown, the next successive supply ports158 of chamber 122 is uncovered while the trailing return port 160 ofchamber 132 is covered and so on through the orbiting movement of thehold-in gear 30.

As can be appreciated by a comparison of FIGS. 3 and 8, the use of aporting arrangement that relies on the angular or circumferentialrelative displacement of the radial slots and ports to produce thesuccessive pressurization of chambers for one of the torque producingfluid motors and the radial or in-and-out relative displacment of thecircumferential slots and ports to produce the successive pressurizationof chambers of the hold-in fluid motor is very advantageous, since theextreme displacements of each of these motions lags the other by 90 asthe assembly 22 orbits about the output gear 12 axis. Thus the optimumarrangement of a pure torque producing vector and a pure hold-in vectorwhich would be at right angles to each other as shown in FIGS. 4 and 9,is inherently capable of being produced by this porting arrangment.Furthermore, the full relative motion of the orbiting gears and thestationary plate is available to perform the porting function to therebymaximize the usable port sizes and minimize fluid losses therethrough.

It can also be appreciated from this description that purely fluidpressure forces are used in maintaining these gears in mesh, and thatdrive through the unit can be shut down very simply by discontinuing thesupply of fluid to the hold-in fluid motor 36, as the demeshing forceswill immediately tend to cause the assembly 22 including the internallytoothed sleeve 24 attached gears 26, 28, and 30 to move so as to becentered with respect to the reaction gears as well as the outer gear12. This produces a decoupling of the output gear 12 from the sleeve 24as shown in FIG. 13 as well as blocking of all the ports of the fluidmotors 32, 34 and 36 to discontinue orbiting movement thereof. In thismode the output shaft 12 can be freely rotated without backdriving anygearing or motor members.

In order to insure accurate centering and secure positioning of theassembly 22 which in the decoupled state would be completelyfree-floating, two sets of centering pistons (three per set) areprovided as shown in FIGS. 5, l0, and 13 in manifolds 72 and 98.

The first set includes three pistons 178, 180, 182, slidably disposed instepped bores 184, 186, and 188 in manifold member 72, and retainedtherein by means of plugs 190, 192, and 194. Compression springs 196,198, 200 bias the respective pistons 178, 180, 182 inwardly toward thesleeve 24.

Annular chambers 202, 204, and 206 are connected to the supply for thehold-in fluid motor 36 via passages 208, 210, 212 (FIGS. 6 and 7)communicating with the supply annulus 164 so that whenever fluid undersufficient pressure is supplied to the hold-in fluid motor 36, thepressure supplied thereby to chambers 202, 204, and 206 causes thepistons to be retracted against the bias of compression springs 196,198, 200 to the position shown in FIG. 5.

The second set of pistons includes three pistons 214, 216, and 218disposed in bores 220, 222, 224 formed in manifold 98 and retainedtherein by means of plugs 226, 228, and 230. Compression springs 232,234, and 236 bias the respective pistons 214, 216, 218 inwardly towardthe sleeve 24.

Annular chambers 238, 240, 242 formed by steps in the bores 220, 222,224 are provided with the hold-in motor 36 supply pressure by means ofpassages (not shown) similar to passages 208, 210, 212 communicatingwith annular groove 244 (FIGS. 1, l1). Annular groove 244 communicateswith the hold-in fluid motor supply annulus 164 by means of passage 246(FIGS. 6, 7), bore 248 in porting plate 146, passage 250 in reactiongear 118, bore 252 in porting plate 148,- and groove 254 (FIGS. 7, 11)in manifold 98.

Thus, in the same fashion as the first piston set, as long as fluidunder sufficient pressure is supplied to the hold-in fluid motor 36,pistons 214, 216, and 218 are able to overcome the spring force actingthereon and are held in the position shown in FIG. 10.

Whenever the pressure declines sufficiently to allow the compressionsprings 234, 236, and 238 to overcome the force created thereby, thepistons will move to seat on shoulders 256, 258, 260 formed in the bores222, 224, and 228, respectively.

In this position, each piston of both sets contacts the sleeve 24 andcauses it to be centered with respect to the axis of the output gear 12as shown in FIG. 13 to effectively decouple the unit from the drivenload.

It is noted that this decoupling is fail-safe as a loss of pressure dueto ruptured lines or other malfunction will automatically cause thiscentering action due to the demeshing forces and the action of thecompression springs.

It is also noted that, as the fluid pressure is used in a static sense,only negligible flow requirements are needed, and hence the hold-insystem does not expend any significant power either in the coupled ordecoupled state.

It can be appreciated that this coupling arrangement also allows thesleeve assembly to be unsupported by bearings and hence substantiallyreduces the inertia and frictional losses of the unit, as well as itscost while increasing its reliability.

While a specific embodiment has been described, the invention is not tobe so limited and many variations are of course possible within thescope of the present invention.

What is claimed is:

1. An actuator comprising:

at least one reaction member having a reaction surface;

an orbiting member floating with respect to said reaction surface ofsaid reaction member;

orbiting means selectively causing said orbiting member to orbit inengagement with said reaction member reaction surface;

an output member and means producing rotation of said output member inresponse to said orbiting movement of said orbiting member including ageared engagement therebetween;

hold-in means separate from said orbiting means producing a force actingon said orbiting member so as to maintain said geared engagement thereofwith said output member during said orbiting of said orbiting member,whereby said floating orbiting member may be maintained in gearedengagement against forces tending to produce disengagement thereof.

2. The actuator of claim 1 wherein said hold-in means includes a fluidmotor and means supplying fluid under pressure thereto producing saidforce on said orbiting member.

3. The actuator of claim 2 wherein said orbiting means includes at leastone fluid motor separate from said hold-in means fluid motor.

4. The actuator of claim 1 further including centering means positioningsaid orbiting member concentrically with respect to said reaction memberand said output member whenever said hold-in force is less than apredetermined magnitude.

5. The actuator of claim 4 wherein said centering means includes atleast one fluid operated device which is biased to tend to produce saidcentering action on said orbiting member but which bias is overcome bysaid fluid under pressure supplied to said hold-in fluid motor if of apredetermined magnitude.

6. The actuator of claim 5 wherein said centering means includes aplurality of fluid operated pistons disposed with their axes about theaxis of said reaction member and means for causing said centering actionof said orbiting member in response to movement of said pistons towardssaid reaction member axis.

7. The actuator of claim 6 wherein said centering means bias is producedby means biasing said pistons towards said reaction member axis andwherein said bias means is overcome by fluid under pressure supplied tosaid hold-in fluid motor.

8. The actuator according to claim 1 wherein said hold-in means includesa hold-in member connected to said orbiting member and orbitingtherewith and wherein said hold-in force is exerted on said hold-inmember.

9. The actuator of claim 8 wherein said hold-in member is disposedwithin a hold-in reaction member and wherein said hold-in means includesa plurality of fluid chambers partially defined by said hold-in memberand hold-in reaction member and further includes means for successivelypressurizing and depressurizing said chambers so as to produce saidforce.

10. The actuator of claim 9 wherein said hold-in means includes portingmeans producing said successive pressurization and depressurization ofsaid fluid chambers in response to said orbiting motion of said hold-inmember.

11. The actuator according to claim 9 wherein said porting meansincludes a stationary hold-in porting plate axially juxtaposed to saidmember having supply and return ports formed therein connected to asupply source and return respectively, and further including recessesformed in said hold-in member cooperating with said ports in saidporting plate to produce said successive pressurization anddepressurization of said chambers.

12. The actuator of claim 11 wherein said orbiting means also includes aplurality of fluid chambers defined in part by said orbiting member andsaid reaction member also includes porting means having a porting platehaving supply and return ports formed therein and recesses in saidorbiting member cooperating to produce said orbiting movement of saidorbiting member by successive pressurization and depressurization ofsaid chambers, and wherein one of said hold-in porting means or orbitingporting means supply and return ports are radially spaced from eachother and the other are circumferentially spaced from each other,whereby said porting means successive pressurization anddepressurization of one said hold-in member or orbiting member iscarried out by radial movement of the holdin or orbiting members and theporting means pressurization and depressurization of the other of saidorbiting as hold-in members is carried out by the circumferentialmovement of the orbiting or hold-in member.

13. The actuator of claim 8 further including a second reaction memberhaving a reaction surface and second orbiting member floating withrespect to said second reaction member and connected to said hold-inmember and said first orbiting member and also further includes a secondorbiting means selectively causing said orbiting member to orbit inengagement with said second reaction member reaction surface.

14. The actuator of claim 13 wherein said hold-in member is connectedbetween said first and second orbiting members.

15. The actuator of claim 14 further including centering means acting onsaid connected orbiting and hold-in members tending to center saidassembly on the axes of said reaction members, said centering meansincluding means for acting on said connected orbiting and hold-inmembers along lines of action in planes between each of said orbitingmembers and said hold-in member.

16. An actuator comprising:

at least one reaction member having a reaction surface;

an orbiting member floating with respect to said reaction surface ofsaid reaction member;

orbiting means selectively causing said orbiting member to orbit inengagement with said reaction member reaction surface;

an output member and means producing rotation of said output member inresponse to said orbiting movement of said orbiting member including ageared engagement therebetween;

fluid hold-in means separate from said orbiting means producing a fluidforce acting on said orbiting member so as to maintain said gearedengagement thereof with said output member during said orbiting of saidorbiting member, whereby said floating orbiting member may be maintainedin geared engagement against forces tending to produce disengagementthereof.

17. The actuator of claim 16 wherein said fluid holdin means includes afluid motor and means supplying fluid under pressure thereto producingsaid force on said orbiting member.

18. The actuator of claim 17 wherein said orbiting means includes atleast one fluid motor.

19. An actuator comprising:

at least one reaction member having a reaction surface;

an orbiting member floating with respect to said reaction surface ofsaid reaction member;

orbiting means selectively causing said orbiting memw ber to orbit inengagement with said reaction member reaction surface;

an output member and means producing rotation of said output member inresponse to said orbiting movement of said orbiting member including ageared engagement therebetween; fluid motor holdin means separate fromsaid orbiting means producing a force on said orbiting member so as tomaintain said geared engagement thereof with said output member duringsaid orbiting of said orbiting member; and

means selectively discontinuing said hold-in force produced by saidhold-in force whereby said floating orbiting member may be maintained ingeared engagement against forces tending to produce disengagementthereof when said hold-in force is produced but is allowed to move outof geared engagement when said hold-in force is discontinued. 20.Theactuator according to claim 19 wherein said hold-in means includes ahold-in member connected to said orbiting member and orbiting therewithand wherein said hold-in force is exerted on said hold-in member.

21. The actuator of claim 19 further including centering meanspositioning said orbiting member concentrically with respect to saidreaction member whenever said hold-in force is discontinued.

22. The actuator of claim 21 wherein said centering means includes atleast one fluid operated device which is biased to tend to produce saidcentering action on said orbiting member but which bias is overcome byfluid under pressure supplied to said hold-in fluid motor if of apredetermined magnitude.

1. An actuator comprising: at least one reaction member having a reaction surface; an orbiting member floating with respect to said reaction surface of said reaction member; orbiting means selectively causing said orbiting member to orbit in engagement with said reaction member reaction surface; an output member and means producing rotation of said output member in response to said orbiting movement of said orbiting member including a geared engagement therebetween; hold-in means separate from said orbiting means producing a force acting on said orbiting member so as to maintain said geared engagement thereof with said output member during said orbiting of said orbiting member, whereby said floating orbiting member may be maintained in geared engagement against forces tending to produce disengagement thereof.
 2. The actuator of claim 1 wherein said hold-in means includes a fluid motor and means supplying fluid under pressure thereto producing said force on said orbiting member.
 3. The actuator of claim 2 wherein said orbiting means includes at least one fluid motor separate from said hold-in means fluid motor.
 4. The actuator of claim 1 further including centEring means positioning said orbiting member concentrically with respect to said reaction member and said output member whenever said hold-in force is less than a predetermined magnitude.
 5. The actuator of claim 4 wherein said centering means includes at least one fluid operated device which is biased to tend to produce said centering action on said orbiting member but which bias is overcome by said fluid under pressure supplied to said hold-in fluid motor if of a predetermined magnitude.
 6. The actuator of claim 5 wherein said centering means includes a plurality of fluid operated pistons disposed with their axes about the axis of said reaction member and means for causing said centering action of said orbiting member in response to movement of said pistons towards said reaction member axis.
 7. The actuator of claim 6 wherein said centering means bias is produced by means biasing said pistons towards said reaction member axis and wherein said bias means is overcome by fluid under pressure supplied to said hold-in fluid motor.
 8. The actuator according to claim 1 wherein said hold-in means includes a hold-in member connected to said orbiting member and orbiting therewith and wherein said hold-in force is exerted on said hold-in member.
 9. The actuator of claim 8 wherein said hold-in member is disposed within a hold-in reaction member and wherein said hold-in means includes a plurality of fluid chambers partially defined by said hold-in member and hold-in reaction member and further includes means for successively pressurizing and depressurizing said chambers so as to produce said force.
 10. The actuator of claim 9 wherein said hold-in means includes porting means producing said successive pressurization and depressurization of said fluid chambers in response to said orbiting motion of said hold-in member.
 11. The actuator according to claim 9 wherein said porting means includes a stationary hold-in porting plate axially juxtaposed to said member having supply and return ports formed therein connected to a supply source and return respectively, and further including recesses formed in said hold-in member cooperating with said ports in said porting plate to produce said successive pressurization and depressurization of said chambers.
 12. The actuator of claim 11 wherein said orbiting means also includes a plurality of fluid chambers defined in part by said orbiting member and said reaction member also includes porting means having a porting plate having supply and return ports formed therein and recesses in said orbiting member cooperating to produce said orbiting movement of said orbiting member by successive pressurization and depressurization of said chambers, and wherein one of said hold-in porting means or orbiting porting means supply and return ports are radially spaced from each other and the other are circumferentially spaced from each other, whereby said porting means successive pressurization and depressurization of one said hold-in member or orbiting member is carried out by radial movement of the hold-in or orbiting members and the porting means pressurization and depressurization of the other of said orbiting as hold-in members is carried out by the circumferential movement of the orbiting or hold-in member.
 13. The actuator of claim 8 further including a second reaction member having a reaction surface and second orbiting member floating with respect to said second reaction member and connected to said hold-in member and said first orbiting member and also further includes a second orbiting means selectively causing said orbiting member to orbit in engagement with said second reaction member reaction surface.
 14. The actuator of claim 13 wherein said hold-in member is connected between said first and second orbiting members.
 15. The actuator of claim 14 further including centering means acting on said connected orbiting and hold-in members tending to center said assembly on the axes of said reaction members, said centerinG means including means for acting on said connected orbiting and hold-in members along lines of action in planes between each of said orbiting members and said hold-in member.
 16. An actuator comprising: at least one reaction member having a reaction surface; an orbiting member floating with respect to said reaction surface of said reaction member; orbiting means selectively causing said orbiting member to orbit in engagement with said reaction member reaction surface; an output member and means producing rotation of said output member in response to said orbiting movement of said orbiting member including a geared engagement therebetween; fluid hold-in means separate from said orbiting means producing a fluid force acting on said orbiting member so as to maintain said geared engagement thereof with said output member during said orbiting of said orbiting member, whereby said floating orbiting member may be maintained in geared engagement against forces tending to produce disengagement thereof.
 17. The actuator of claim 16 wherein said fluid hold-in means includes a fluid motor and means supplying fluid under pressure thereto producing said force on said orbiting member.
 18. The actuator of claim 17 wherein said orbiting means includes at least one fluid motor.
 19. An actuator comprising: at least one reaction member having a reaction surface; an orbiting member floating with respect to said reaction surface of said reaction member; orbiting means selectively causing said orbiting member to orbit in engagement with said reaction member reaction surface; an output member and means producing rotation of said output member in response to said orbiting movement of said orbiting member including a geared engagement therebetween; fluid motor hold-in means separate from said orbiting means producing a force on said orbiting member so as to maintain said geared engagement thereof with said output member during said orbiting of said orbiting member; and means selectively discontinuing said hold-in force produced by said hold-in force whereby said floating orbiting member may be maintained in geared engagement against forces tending to produce disengagement thereof when said hold-in force is produced but is allowed to move out of geared engagement when said hold-in force is discontinued.
 20. The actuator according to claim 19 wherein said hold-in means includes a hold-in member connected to said orbiting member and orbiting therewith and wherein said hold-in force is exerted on said hold-in member.
 21. The actuator of claim 19 further including centering means positioning said orbiting member concentrically with respect to said reaction member whenever said hold-in force is discontinued.
 22. The actuator of claim 21 wherein said centering means includes at least one fluid operated device which is biased to tend to produce said centering action on said orbiting member but which bias is overcome by fluid under pressure supplied to said hold-in fluid motor if of a predetermined magnitude. 